Chart readme fixes

[scottrigby]

What this PR does / why we need it:

1. Removes redundant URL in favor of zero-downtime section header anchor, which I meant to do in Document migration path to ingress-nginx chart from stable/nginx-ingress #6038
2. Direct link to index.yaml for easy browsing by end users without CLI
3. Fix YAML linting

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Which issue/s this PR fixes

How Has This Been Tested?

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added tests to cover my changes.
• All new and existing tests passed.

[aledbf]

/lgtm
/approve

[aledbf]

@scottrigby thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, scottrigby

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